Transition-metal-catalyzed carbenoid reactions of sulfonium ylides

Article abstract of DOI:10.1002/(SICI)1522-2675(19990609)82:6<935::AID-HLCA935>3.0.CO;2-X

Olefins undergo cyclopropanation with diphenylsulfonium (ethoxycarbonyl)methylide (=diphenyl-sulfonium 2-ethoxy-2-oxoethylide; 3a) in the presence of chiral Cu(I) or Rh(II) catalysis, trans/cis Ratios and ee's of the cyclopropanes 6 obtained with this ylide in the presence of a chiral Cu(I) catalyst 7 are identical with those obtained with ethyl diazoacetate (4). In the case of catalysis with Rh(II), the trans/cis ratios of the cyclopropanes as well as the enantioselectivity change slightly upon going from the ylide 3a to diazoacetate 4.

Full text of DOI:10.1002/(SICI)1522-2675(19990609)82:6<935::AID-HLCA935>3.0.CO;2-X

Helvetica Chimica Acta ± Vol. 82 (1999)
935
Transition-Metal-Catalyzed Carbenoid Reactions of Sulfonium Ylides
by Paul Müller*, Daniel Fernandez, Patrice Nury, and Jean-Claude Rossier
Department of Organic Chemistry, University of Geneva,
30, Quai Ernest-Ansermet, CH-1211 Geneva 4
Olefins undergo cyclopropanation with diphenylsulfonium (ethoxycarbonyl)methylide (ˆdiphenyl-
sulfonium 2-ethoxy-2-oxoethylide; 3a) in the presence of chiral CuI or RhII catalysts. trans/cis Ratios and eeꢀs
of the cyclopropanes 6 obtained with this ylide in the presence of a chiral CuI catalyst 7 are identical with those
obtained with ethyl diazoacetate (4). In the case of catalysis with RhII, the trans/cis ratios of the cyclopropanes
as well as the enantioselectivity change slightly upon going from the ylide 3a to diazoacetate 4.
1. Introduction. ± Sulfur ylides react with carbonyl groups or with electron-deficient
CˆC bonds in a two-step reaction to afford epoxides or cyclopropanes, respectively [1].
With enantiomerically pure ylides, asymmetric cyclopropanation of CˆO [2][3] and
CˆC bonds [4] is possible. In contrast, simple olefins are unreactive towards sulfur
ylides. However, when decomposed in the presence of olefins under thermal or
photochemical conditions, or in the presence of transition metals, sulfur ylides provide
cyclopropanes possibly derived from intermediate carbenes or carbenoids [5]. Based
Á
on previous studies of Cohen et al. [6], Cimetiere and Julia [7] recently proposed
diphenylsulfonium (methoxycarbonyl)methylide as a substitute for methyl diazoace-
tate in copper-catalyzed cyclopropanations of olefins. The mechanism of the reaction of
the ylide was not established, but the results imply a carbene or a carbenoid
intermediate. Such intermediates have also been invoked to rationalize the formal
intramolecular NH insertion resulting upon exposure of sulfoxonium ylides to
[Rh2(OAc)4] [8]. The generation of metal carbenoids from ylides is of interest in the
context of asymmetric carbene transfer reactions [9], because it could allow the
replacement of the potentially explosive, toxic, and/or carcinogenic diazo compounds
[10] which are traditionally used as carbenoid precursors. In a previous communication,
we have shown that RhII-catalyzed decomposition of diazo compounds and of the
corresponding phenyliodonium ylides affords identical product mixtures and proceeds
in both cases via RhII carbenoids [11]. Thus, phenyliodonium ylides may be substitutes
for diazo compounds in metal-catalyzed carbenoid transformations. However, the use
of iodonium ylides is limited. Phenyliodonium ylides must be stabilized by two
electron-attracting substituents, such as carbonyl or sulfonyl groups, in order to be
isolable. Monocarbonyliodonium ylides have only very recently been characterized;
they are stable in THF below 308, and no metal-catalyzed reactions of monocarbo-
nyliodonium ylides have yet been reported [12]. Sulfur ylides do not suffer this
limitation. They are isolable and well characterized, and may be manipulated at room
temperature, even when stabilized by only one electron-attracting substituent [1][7].
We have now investigated the CuI- or RhII-catalyzed decomposition of diphenylsulfo-

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Helvetica Chimica Acta ± Vol. 82 (1999)
nium (ethoxycarbonyl)methylide (ˆdiphenylsulfonium 2-ethoxy-2-oxoethylide; 3a) in
the presence of olefins with the hope of developing a synthetic alternative for carbenoid
olefin cyclopropanation. A comparison of the trans/cis ratios and enantiomeric excesses
(eeꢀs) of the resulting cyclopropanes with those obtained upon metal-catalyzed olefin
cyclopropanation with ethyl diazoacetate (EDA, 4) was expected to provide conclusive
evidence for metal-carbenoid intermediates in the reaction of the ylide.
2. Results and Discussion. ± 2.1. Synthesis of Diphenylsulfonium (Ethoxycarbo-
nyl)methylide (3a) and Dimethylsulfonium (Ethoxycarbonyl)methylide (3b). Diphe-
nylsulfonium (ethoxycarbonyl)methylide (3a) was prepared by a slightly modified
version of the procedure originally proposed by Nozaki et al. [13]. Reaction of diphenyl
sulfide (1a) with ethyl bromoacetate in the presence of AgBF4 in the dark afforded the
sulfonium salt 2a, which was deprotonated with Et3N in EtOH at 08 to afford 3a in 75%
yield (Scheme 1). The ylide 3a is relatively stable. No change was detected in the
1H-NMR spectrum after 24 h in CDCl3 at 258. After 4 days, signals of diphenyl sulfide,
ethyl maleate, and ethyl fumarate (maleate/fumarate 6 :1) started to appear. No
decomposition occurred in CH2Cl2 within 13 h in the presence of [Rh2(OAc)4] (1 mol-
%) at 258, and only trace amounts of cyclopropanes were formed upon attempted
cyclopropanation of styrene (5a) with 3a in the presence of [Rh2(OAc)4] in refluxing
CH2Cl2. Carbene addition occurred, however, upon slow addition (syringe pump, 16 h)
of 3a to olefins (10 equiv.) in refluxing 1,2-dichloroethane (DCE) containing 2 mol-%
of [Cu(acac)2] or [Rh2(OAc)4].
Scheme 1
Dimethylsulfonium (ethoxycarbonyl)methylide (3b) was prepared by reaction of
ethyl bromoacetate with dimethyl sulfide (1b), as described by Johnson and Amel for
the corresponding methyl ester [14]. The resulting sulfonium salt 2b was deprotonated
with NaH to yield 3b. Preliminary experiments, directed towards decomposition of 3b
with [Rh2(OAc)4] in the presence of styrene (5a), provided none of the expected
cyclopropanes. In the light of these negative results, the chemistry of 3b was not further
investigated.
2.2. Copper(I)-Catalyzed Cyclopropanation of Olefins. Some representative olefins
were subjected to intermolecular cyclopropanation by syringe-pump addition of the
ylide 3a or ethyl diazoacetate (EDA; 4) to a solution of olefin 5a ± h (10 equiv.) and 2%
of the chiral Cu-semicorrin catalyst 7 of Pfaltz and co-workers [15] (Scheme 2). For
practical reasons, the reactions of 3a and 4 could not be carried out under exactly
identical conditions: since 3a reacted only at elevated temperature, the cyclopropa-
nations were carried out in refluxing 1,2-dichloroethane (DCE), at 828. At this

Helvetica Chimica Acta ± Vol. 82 (1999)
937
temperature, however, partial decomposition of the catalyst was observed in the
reaction with EDA (4), as evidenced by a progressive decrease with time of the
enantiomeric excess of the cyclopropanes 6 when samples were withdrawn from the
reaction mixture during addition of EDA. This phenomenon was, however, not
observed in the cyclopropanations with 3a. Reactions with EDA (4) were, therefore,
carried out at room temperature (238), and those with 3a at 828. Table 1 summarizes the
principal results. The reactions of 3a and 4 differ significantly with respect to the yield,
which is always lower when the ylide is used as carbene precursor. Disubstituted olefins
proved to be particularly unreactive in the Cu-catalyzed cyclopropanation with 3a.
Thus, (E)-b-methylstyrene (ˆ(E)-(prop-1-enyl)benzene; 5e; R1 ˆ Ph, R2 ˆ H, R3 ˆ
Me) afforded only a 20% yield of cyclopropanes, and only traces of cyclopropanes were
formed upon reaction of (E)-pent-2-ene (5g; R1 ˆ Et, R2 ˆ H, R3 ˆ Me) or (Z)-hex-3-
ene in the presence of the chiral catalyst 7. (Z)-b-Methylstyrene (5h; R1 ˆ Ph, R2 ˆ Me,
R3 ˆ H) was equally unreactive and afforded only trace amounts of cyclopropanes with
[Cu(acac)2]. With these unreactive olefins, formation of the formal carbene dimers
dimethyl fumarate and maleate predominated. When cyclopropanations with EDA (4)
were performed at 508, the enantioselectivity was significantly below that observed at
258, and also below that resulting from reaction with the ylide 3a at 828.
The relative and absolute configurations of the cyclopropanecarboxylates 6
prepared in this study have been assigned previously by other investigators (see
Exper. Part). The ylide 3a and EDA (4) afforded cyclopropanes of identical absolute
configurations with all of the olefins investigated. Despite the variation in reaction
temperature, the variation of the trans/cis ratios of the cyclopropanes resulting from
Scheme 2
a
)
See Tables 1 and 2 for R1, R2, and R3.

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 1. Selectivity for Cyclopropanation of Olefins 5 with Ph2SˆCHCO2Et (3a) or EDA (4) Catalyzed by the
Cu-Semicorrin Complex 7a)
Olefin R1
R2 R3
3a, 4
6
X ˆ T [8C] Yield [%] trans/cis ee (trans) [%]
ee (cis) [%]
5a
5a
5a
5b
5b
5b
5c
5c
5c
5d
5d
5e
5e
5e
5f
5f
Ph
Ph
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
N2
N2
Ph2S 82
N2
N2
Ph2S 82
N2
N2
Ph2S 82
N2 23
Ph2S 82
23
50
75
53
31
20
37
20
52
57
24
65
55
42
59
20
50
28
75 : 25
71 : 29
77: 23
72 : 28
71 : 29
68 : 32
61 : 39
58 : 42
60 : 40
58 : 42
59 : 41
70 : 30
68 : 32
65 : 35
30 : 70
28 : 72
78 (1S,2S)
74 (1S,2S)
71 (1S,2S)
63 (1S,2S)
76 (1S,2S)
72 (1S,2S)
70 (1S,2R)
37 (1S,2R)
76 (1S,2R)
45 (1S,2R)
15 (1S,2R)
5 (1S,2S,3S)
10 (1S,2S,3S)
7 (1S,2S,3S)
54 (1S,2R)
56 (1S,2R)
59 (1S,2R)
70 (1S,2R)
69 (1S,2R)
59 (1S,2R)
77 (1S,2S)
41 (1S,2S)
80 (1S,2S)
65 (1S,2S)
75 (1S,2S)
48 (1S,2R,3R)
32 (1S,2R,3R)
50 (1S,2R,3R)
C5H11
C5H11
C5H11
H2CˆCH
H2CˆCH
H2CˆCH
Me2CˆCH
Me2CˆCH
Ph
Ph
Ph
C3H6
C3H6
23
50
23
50
H
H
H
Me
Me
Me
N2
N2
23
50
Ph2S 82
23
Me3SiO Ph2S 82
Me3SiO N2
18(1R,5S,6S)b) 65 (1S,5R,6S)b)
30 (1R,5S,6S)b) 64 (1S,5R,6S)b)
a) 1.0 mmol of 3a or 4 in 5 ml of DCE was added within 16 h to 10 mmol of olefin 5 in 10 ml of DCE at the
temperature indicated. Initiation of the reaction of 3a with a small amount of EDA [15]. b) Enantiomer of 6f.
cyclopropanation with 3a and 4 was small (1 ± 5%). The enantioselectivities changed
slightly more in going from 3a to 4 (2 ± 9%), but the variations were within the
experimental uncertainties, and no clear trend could be identified.
These observations suggest that the Cu-catalyzed cyclopropanations with 3a and 4
proceed by the same reaction mechanism. Since the intermediacy of a Cu-complexed
carbene in the asymmetric olefin cyclopropanation with EDA is established [15], the
same should hold for the reaction with 3a. The formation of carbene dimers upon
attempted cyclopropanation of 1,2-disubstituted olefins suggests an unfavorably high
reactivity of 3a towards the metal-complexed carbene in comparison to olefin
reactivity. Carbene dimers are frequently found, even in carbenoid reactions of diazo
compounds, but owing to the high olefin reactivity towards the metal carbenoid, it
usually represents no serious problem in cyclopropanations. In the case of 3a, however,
the formation of carbene dimers becomes competitive even with terminal olefins, and
this limits the potential of the system.
2.3. Rhodium(II)-Catalyzed Cyclopropanation of Olefins. No cyclopropanation
took place when dimethylsulfonium ylide 3b was exposed to [Rh2(OAc)4] in the
presence of olefins. However, slow addition (16 h) of the diphenyl derivative 3a in
refluxing DCE in the presence of [Rh2(OAc)4] (2 mol-%) and styrene (5a) afforded
cyclopropanes 6a in 38% yield and with a trans/cis ratio of 52 :48 (Table 2). All of the
ylide had reacted after this time, and the yield of carbene dimers was below 3%. As in
the case of the Cu-catalyzed cyclopropanation of styrene (5a), the yield with 3a was
lower than that obtained with EDA (4) in the reaction catalyzed with [Rh2(OAc)4].
The observation of reduced yields with 3a applies generally, and was particularly
significant with di- and trisubstituted olefins as substrates. In these reactions, formation

Helvetica Chimica Acta ± Vol. 82 (1999)
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of formal carbene dimers predominated. The trans/cis ratio of the cyclopropanes 6a
derived from styrene deviated slightly, but reproducibly from that of 60 :40 obtained
with EDAunder the same conditions, and from the 62 :38 ratio reported for EDA (4) in
CH2Cl2 at 258 [16]. Originally, we thought that this change was due to complexation of
one of the vacant coordination sites of the rhodium complex by diphenyl sulfide (1a),
which is liberated in the course of the reaction of the ylide 3a [11b]. However, the trans/
cis ratio of cyclopropanes derived from other olefins remained unchanged upon
replacement of 3a by 4. The cyclopropanation of 5a and some other olefins with 3a and
4 was also carried out in the presence of Ph2S with the expectation that this addition
would result in modification of the trans/cis ratios, but no unambiguous results could be
obtained from these experiments (see Tables 2 and 3). While the RhII-catalyzed
reactions exhibited somewhat stronger variations in the diastereo- and enantioselec-
tivities between 3a and 4, the origin of the trend could not be detected.
Table 2. [Rh2(OAc)4]-Catalyzed Cyclopropanation of Olefins 5 with Ph2SˆCHCOOEt (3a) and EDA (4)a)
Olefin
No.
3a,4
6
Comment
X ˆ
Yield [%]
trans/cis
Styrene
Styrene
Styrene
Styrene
Hept-1-ene
Hept-1-ene
Buta-1,3-diene
Buta-1,3-diene
(E)-b-Methylstyrene
(E)-b-Methylstyrene
1-(Me3SiO)-cyclopentene
1-(Me3SiO)-cyclopentene
(E)-Pent-2-eneb)
(E)-Pent-2-eneb)
(Z)-b-Methylstyrenec)
(Z)-b-Methylstyrenec)
(Z)-b-Methylstyrenec)
(Z)-b-Methylstyrenec)
5a
5a
5a
5a
5b
5b
5c
5c
5e
5e
5f
N2
Ph2S
N2
Ph2S
N2
Ph2S
N2
Ph2S
N2
Ph2S
N2
Ph2S
N2
Ph2S
N2
61
38
±
60 : 40
52 : 48
60 : 40
57: 43
59 : 41
57: 43
45 : 55
43 : 57
77: 23
59 : 41
47: 53
45 : 55
56 : 44
52 : 48
77: 23
66 : 34
62 : 38
69 : 31
1 equiv. of Ph2S before addition
1 equiv. of Ph2S before addition
±
50
23
36
30
51
3
42
9
5f
5g
5g
5h
5h
5h
5h
43
20
50
25
50
3
N2
N2
Ph2S
1 equiv. of Ph2S before addition
1 equiv. of Ph2S during addition
a) Conditions: Syringe-pump addition of 3a or 4 (1 mmol) in DCE (5.0 ml) to olefin 5 (10 mmol) in refluxing
b
c
DCE (10 ml) containing the catalyst (0.02 mmol). ) R1 ˆ Et, R2 ˆ H, R3 ˆ Me. ) R1 ˆ Ph, R2 ˆ Me, R3 ˆ H.
The cyclopropanation of several olefins with 3a and EDA (4) was investigated with
three chiral RhII catalysts, namely [Rh2{(2S)-mepy}4] (8), [Rh2{( )-(R)-bnp}4] (9), and
[Rh2{( )-(S)-ptpa}4] (10) (Table 3). The enantioselectivity of the cyclopropanation
was generally poor, except with [Rh2{(2S)-mepy}4], where the results with EDA (4)
were consistent with reported data [16]. Again, we found some unexpected variations
in the results obtained with 3a and 4 for which there is no rationalization.
2.4. Intramolecular Carbenoid Reactions with Diphenylsulfonium (Alkoxycarbo-
nyl)methylides. The most successful applications of chiral rhodium carboxamidate
catalysts are found in the field of intramolecular cyclopropanation and CH insertion.
Thus, allyl diazoacetate (15) undergoes cyclopropanation to 14 in the presence of

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 3. Cyclopropanation of Olefins 5 with Ph2SˆCHCOOEt (3a) and EDA (4) in the Presence of Optically
Active RhII Complexesa)
Olefin
No. Catalyst
3a,4 6
X ˆ Yield [%] trans/cis ee (trans) [%] ee (cis) [%]
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Hept-1-ene
Hept-1-ene
Hept-1-ene
Hept-1-ene
Buta-1,3-diene
Buta-1,3-diene
Buta-1,3-diene
Buta-1,3-diene
5a [Rh2{(2S)-mepy}4] N2 20
5a [Rh2{(2S)-mepy}4] N2 59b)
5a [Rh2{(2S)-mepy}4] Ph2S 34
5a [Rh2{( )-(R)-bnp}4] N2 45
5a [Rh2{( )-(R)-bnp}4] Ph2S 47
5a [Rh2{( )-(S)-ptpa}4] N2 57
5a [Rh2{( )-(S)-ptpa}4] Ph2S 35
5b [Rh2{(2S)-mepy}4] N2 41
5b [Rh2{(2S)-mepy}4] Ph2S 14
5b [Rh2{( )-(R)-bnp}4] N2 52
5b [Rh2{( )-(R)-bnp}4] Ph2S 10
5c [Rh2{(2S)-mepy}4] N2 25
5c [Rh2{(2S)-mepy}4] Ph2S 21
5c [Rh2{( )-(S)-ptpa}4] N2 60
5c [Rh2{( )-(S)-ptpa}4] Ph2S 18
52 : 48 54 (1S,2S)
56 : 44b) 58 (1S,2S)b)
67: 33 48 (1S,2S)
38 (1S,2R)
33 (1S,2R)b)
34 (1S,2R)
3 (1R,2S)c)
2 (1S,2R)
2 (1S,2R)
2 (1R,2S)c)
40 (1S,2R)
19 (1S,2R)
4 (1S,2R)
4 (1S,2R)
44 (1S,2S)
39 (1S,2S)
5 (1S,2S)
50 : 50
60 : 40
47: 53
52 : 48
5 (1R,2R)c)
0
2 (1S,2S)
0
54 : 46 42 (1S,2S)
49 : 51 13 (1S,2S)
56 : 44
59 : 49
4 (1S,2S)
2 (1S,2S)
44 : 56 39 (1S,2R)
42 : 58 34 (1S,2R)
51 : 49
55 : 45
3 (1S,2R)
0
2 (1S,2S)
1-(Me3SiO)-Cyclopentene 5f [Rh2{(2S)-mepy}4] N2 33
61 : 39 16 (1R,5S,6S)d) 8 (1S,5R,6S)d)
55 : 45 23 (1R,5S,6S)d) 39 (1S,5R,6S)d)
58 : 42 15 (1S,2S,3S) 13 (1S,2R,3S)
56 : 44 13 (1S,2S,3S) 12 (1S,2R,3S)
1-(Me3SiO)-Cyclopentene 5f [Rh2{(2S)-mepy}4] Ph2S
5
(E)-Pent-2-enee)
(E)-Pent-2-enee)
5g [Rh2{(2S)-mepy}4] N2 21
5g [Rh2{(2S)-mepy}4] Ph2S 13
a) Conditions: syringe-pump addition of 3a or 4 (1.0 mmol) in DCE (5.0 ml) to olefin 5 (10 mmol) in refluxing
DCE (10 ml) containing the catalyst. b) In CH2Cl2, under reflux. c) Enantiomer of 6a. d) Enantiomer of 6f.
e) R1 ˆ Et, R2 ˆ H, R3 ˆ Me.
[Rh2{(2S)-mepy}4] (8) in 75% yield and with 95% ee in CH2Cl2 at 258 [17] (see
Table 4). As expected, the enantioselectivity of the reaction decreased to 80%, when it
was carried out in refluxing DCE (Table 4). The allylic ylide 13a was synthesized by
reaction of bromoacetyl bromide with allyl alcohol (ˆ prop-2-en-1-ol). The resulting
ester 11a was converted to the sulfonium salt 12a with Ph2S (1a) and AgBF4, and 12a
was deprotonated with Et3N [18]. The intramolecular cyclopropanation of 13a with
[Rh2{(2S)-mepy}4] (8) in refluxing DCE produced 14 in 40% yield and with 69% ee.
Table 4. Intramolecular Carbenoid Reactions of Ylides 13a and 13b and Diazoacetates 15 and 17
No. R
X
Catalyst
Conditions
Product Yield cis/
[%] trans
ee
[%]
13a CH2ˆCHCH2 Ph2S [Rh2(OAc)4]
DCE, 828
14
14
14
14
30
40
75
68
±
±
±
±
±
13a CH2ˆCHCH2 Ph2S [Rh2{(2S)-mepy}4] DCE, 828
15 CH2ˆCHCH2 N2 [Rh2{(2S)-mepy}4] DCE, 828
15 CH2ˆCHCH2 N2 [Rh2{(2S)-mepy}4] DCE, 828,
69 (1R,5S)
80 (1R,5S)
81 (1R,5S)
‡ 1 equiv. of Ph2S
15 CH2ˆCHCH2 N2 [Rh2{(2S)-mepy}4] CH2Cl2, 258
14
16
16
16
16
75a)
±
95 (1R,5S)a)
13b Cyclohexyl
17 Cyclohexyl
17 Cyclohexyl
17 Cyclohexyl
Ph2S [Rh2{(2S)-mepy}4] DCE, 828
N2 [Rh2{(2S)-mepy}4] DCE, 828
N2 [Rh2{(2S)-mepy}4] CH2Cl2, 258
8.5 73 : 27 93 (cis)b), 85 (trans)
11
65
46
68 : 32 88 (cis), 77 (trans)
75 : 25 97 (cis), 91 (trans)
40 : 60c)
N2 [Rh2(OAc)4]
CH2Cl2, 258
a) See [17]. b) Absolute configuration (3aS,7aS) [17][27]. c) See [28].

Helvetica Chimica Acta ± Vol. 82 (1999)
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Scheme 3
The enantioselectivity was not affected when the reaction of the diazo compound 15
was carried out in the presence of added Ph2S. An attempt to repeat the above sequence
with the ylide derived from 3-methylbut-2-en-1-ol failed. The reaction of 3-methylbut-
2-en-1-ol with bromoacetyl bromide in the presence of AgBF4 produced only
decomposition products, and the desired sulfonium salt could not be obtained.
By analogy, the ylide 13b was synthesized from cyclohexanol via 11b and 12b.
Cyclohexyl diazoacetate (17) reportedly reacts with [Rh2{(2S)-mepy}4] (8) to form the
corresponding lactone 16 as a 75 :25 cis/trans mixture in 65% yield and with eeꢀs of
97% (cis-16) and 91% (trans-16), respectively [9c] [19] (see Table 4). In refluxing
DCE, the yield decreased dramatically to 11%, the cis/trans ratio changed to 68 :32,
and the ee decreased to 88% (cis-16) and 77% (trans-16) (see Table 4). Exposure of the
ylide 13b to [Rh2{(2S)-mepy}4] (8) afforded the lactone 16 in a poor 9% yield as a 73 :27
cis/trans mixture with eeꢀs of 93 (cis-16) and 85% (trans-16). Formation of carbene
dimers predominated largely over the intramolecular insertion.
3. Conclusions. ± The product distribution for the CuI- and RhII-catalyzed
decomposition of diphenylsulfonium ylides and the corresponding diazo compounds
is practically identical, which suggests that both types of compounds react via the same
mechanism. The implication of metal carbenoids as reactive intermediates in both
reactions follows from extensive studies on transition-metal-catalyzed diazo decom-

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position. This hypothesis is supported by the observation of enantiomerically enriched
insertion products upon reaction of the ylide 13b. However, the reactions of the ylides
suffer generally from significantly lower yields in comparison to those of diazo
compounds, and this problem must be overcome in order to allow their use as
substitutes for the latter.
Financial support of this work by the Swiss National Science Foundation (Grant No. 20-45255.95, 20-
48156.96 and 20-52581.97) is gratefully acknowledged.
Experimental Part
1. General. See [20].
2. Sulfonium Ylides. 2.1. Diphenylsulfonium 2-Ethoxy-2-oxoethylide (3a). (2-Ethoxy-2-oxoethyl)diphenyl-
sulfonium Tetrafluoroborate (2a) [18]. Solid AgBF4 (5.0 g, 25 mmol) was added within 4 min to bromoacetate
(16 ml, 10 equiv.) and Ph2S (4.78 g, 25 mmol) in a round-bottomed flask wrapped with aluminum foil. The soln.
was stirred at r.t. for 2 h. The precipitate of AgBr was removed by filtration through Celite. The residue of the
filtrate was extracted with CH2Cl2 (15 ml) and the org. phase dried (MgSO4) and evaporated. The residue was
recrystallized from EtOH: 2a (5.25 g, 56%) M.p. 108 ± 1108. IR (CHCl3): 3450w, 2465m, 1724m, 1617s, 1067s,
1580m, 1476m, 1443m, 1322s, 1134s. 1H-NMR (CDCl3, 400 MHz): 1.13 (t, J ˆ 7, 3 H); 4.15 (q, J ˆ 7, 2 H); 5.18
(s, 1 H); 7.60 ± 7.71 (m, 6 H); 7.97 ± 8.05 (m, 4 H). 13C-NMR (100 MHz, CDCl3): 13.6 (q); 47.3 (t); 63.8 (t);
‡
124.1 (s); 130.5 (d); 131.4 (d); 134.6 (d); 162.8 (s). MS (electrospray): 273.1 (M ). Anal. calc. for C16H17BFSO2:
C 53.36, H 4.76; found: C 53.24, H 4.87.
Ethylide 3a [13]. To 2a (2.92 g, 8.0 mmol) in EtOH (250 ml) at 08, Et3N (1.62 g, 16 mmol) in EtOH (50 ml)
was added slowly. After 2 h of stirring, H2O (700 ml) was added, the org. layer separated, the aq. phase extracted
with CH2Cl2 (3 Â 150 ml) and the combined org. phase dried and evaporated: 3a (1.82 g, 83%). Yellowish oil. IR
(CHCl3): 3066w, 2995m, 1618s, 1580m, 1478w, 1444w, 1396w, 1371s, 1323m, 1233w, 1134s, 1062w, 1023w, 1023w,
1
1000w, 901w, 855w. H-NMR (200 MHz, CDCl3): 1.22 (t, J ˆ 7.1, 3 H); 3.30 ± 3.50 (br. s, 1 H); 4.09 (q, J ˆ 7.1,
2 H); 7.40 ± 7.59 (m, 10 H). 13C-NMR (50 MHz, CDCl3): 14.9 (q); 58.5 (t); 77.2 (d); 127.9 (d); 130.8 (d); 136.6
(s); 170.0 (s).
2.2. Dimethylsulfonium 2-Ethoxy-2-oxoethylide (3b). The ylide was prepared according to [14].
2.3. Diphenylsulfonium 2-Oxo-2-(prop-2-enyloxy)ethylide (13a). Prop-2-enyl Bromoacetate (11a) [21]. To
prop-2-en-1-ol (10.0 g, 170 mmol) in CH2Cl2 (60 ml) at 608, bromoacetyl bromide (34.8 g, 170 mmol) was
added within 2 h. The temp. was allowed to rise to 258, and the mixture was stirred for 24 h and then treated with
sat. NaHCO3 soln. (100 ml). The org. layer was washed with H2O (2 Â 100 ml), dried (Na2SO4), and
evaporated, and the crude product was distilled at 738/10 Torr: 11a (17.1 g, 56%). Colorless liquid. IR (CHCl3):
2962w, 1738s, 1421m, 1279s, 1165s, 987m. 1H-NMR (200 MHz, CDCl3): 3.85 (s, 2 H); 4.42 (d, J ˆ 5.7, 2 H);
5.20 ± 5.50 (m, 2 H); 5.80 ± 6.00 (m, 1 H). 13C-NMR (50 MHz, CDCl3): 25.7 (t); 31.1 (t); 34.8 (t); 66.7 (t); 119.2
(t); 131.2 (d); 166.9 (s).
[2-Oxo-2-(prop-2-enyloxy)ethyl]diphenylsulfonium Tetrafluoroborate (12a). To 11a (18 g, 100 mmol) and
Ph2S (4.78 g, 25.7 mmol) under N2, anh. AgBF4 (5.00 g, 25 mmol) was added within 2 min at 408. The brown
suspension was stirred at r.t. for 14 h, then diluted with CH2Cl2, and filtered through Celite. After evaporation of
the solvent, the excess of 11a was eliminated by flash distillation. The solid residue was isolated after filtration
and dissolved in a minimum quantity of hot EtOH, the soln. was filtered, the filtrate allowed to cool slowly, and
the precipitated colorless crystals filtered off: 12a (5.63 g, 59%). M.p. 84 ± 868. IR (CHCl3): 3563w, 3034s, 1740s,
1448w, 1311w, 1189m, 1069s. 1H-NMR (400 MHz, CDCl3): 4.59 (d, J ˆ 6, 2 H); 5.14 ± 5.23 (m, 4 H); 5.79
(ddt, J ˆ 6, 10, 17, 1 H); 7.61 ± 7.72 (m, 6 H); 7.96 ± 8.03 (m, 4 H). 13C-NMR (100 MHz, CDCl3): 47.3 (t); 68.0
‡
(t); 119.9 (t); 124.0 (s); 130.3 (d); 130.6 (d); 131.5 (d); 134.7 (d); 162.7 (s). MS (electrospray): 284.7 (M ). Anal.
calc. for C17H17BF4SO2: C 54.86, H 4.60; found: C 54.72, H 4.72.
Ethylide 13a. The general procedure of [13] was used: To 11a (1.00 g, 2.70 mmol) in EtOH (80 ml), Et3N
(1.5 ml, 10.8 mmol) in EtOH (50 ml) was added dropwise at 08. The resulting mixture was kept at 08 for 2 h and
then poured on ice-water (500 g). The white suspension was extracted with CH2Cl2 (3 Â 100 ml) and the extract
dried (MgSO4) and evaporated: 13a (66 mg, 86%). Viscous, yellowish oil which solidified at 188. IR (CHCl3):
3086w, 2955m, 1698s, 1550m, 1435w, 1376w, 1331m, 1233w, 1134m, 1052w, 1012w, 1004w, 755w. 1H-NMR
(200 MHz, CDCl3): 3.50 (br. s, 1 H); 4.53 ± 4.59 (m, 2 H); 5.20 (dd, J ˆ 30, 16, 2 H); 5.85 ± 6.10 (m, 1 H); 7.39 ±
7.60 (m, 10 H). 13C-NMR: 46.2 (t); 65.9 (d); 116.4 (t); 127.9 (d); 129.6 (d); 130.8 (d); 134.5 (d); 136.5 (s); 169.9

Helvetica Chimica Acta ± Vol. 82 (1999)
943
(s). MS: 188(6), 187(18), 186(100), 185(58), 184(27), 183(5), 152(6), 109(5), 99(12), 92(12), 77(9),
77(13), 65(7), 51(17), 50(5).
2.4. Diphenylsulfonium 2-(Cyclohexyloxy)2-oxoethylide (13b). Cyclohexyl Bromoacetate (11b). Phospho-
tungstic acid (H3[P(W3O10)4] ´ H2O; 0.20 g, 0.07 mmol), bromoacetic acid (500 ml), and cyclohexanol (65.1 g,
0.65 mol) were refluxed in toluene (50 ml) under a Dean-Stark trap for 4.5 h [21]. The mixture was then washed
with H2O (100 ml), sat. NaHCO3 soln. (2 Â 100 ml), and H2O (100 ml), dried (MgSO4), and evaporated and
the crude product distilled at 50 ± 608/0.3 Torr: 11b (85.4 g, 78%). Colorless liquid. IR (CHCl3): 2894s, 2861m,
1726s, 1450w, 1421w, 1289s, 1224w, 1174m, 1111w, 1036w, 1010m, 971w, 892w. 1H-NMR (400 MHz, CDCl3):
1.20 ± 1.60 (m, 6 H); 1.65 ± 1.80 (m, 2 H); 3.80 (s, 2 H); 4.75 ± 4.85 (m, 1 H). 13C-NMR (100 MHz, CDCl3): 23.5
(t); 25.2 (t); 26.4 (t); 74.7 (d); 166.6 (s).
[2-(Cyclohexyloxy)-2-oxoethyl]diphenylsulfonium Tetrafluoroborate (12b). To Ph2S (4.55 g, 24.4 mmol) in
11b (45.7 g, 250 mmol) under N2, anh. AgBF4 (5.00 g, 25 mmol) was added within 2 min. The resulting
suspension was stirred in the dark for 50 h and then for 4 d in the daylight (to allow decomposition of traces of
unreacted AgBF4). After dilution with CH2Cl2, the mixture was filtered through Celite, the filtrate evaporated,
and the resulting mixture of crystals and liquid cooled to 48. The crystals were separated by filtration and
purified by recrystallization from EtOH: 6.634 g (66%) or 12b. M.p. 142 ± 1448. IR (CHCl3): 3564w, 3029m,
2942m, 1730s, 1448m, 1309m, 1227w, 1210s, 1066s, 912w. 1H-NMR (400 MHz, CDCl3): 1.10 ± 1.40 (m, 5 H);
1.41 ± 1.48 (m, 1 H); 1.54 ± 1.62 (m, 2 H); 4.70 ± 4.79 (m, 1 H); 5.15 (s, 2 H); 7.61 ± 7.71 (m, 6 H); 7.97 ± 8.04
(m, 4 H). 13C-NMR (100 MHz, CDCl3): 23.3 (t); 24.9 (t); 30.9 (t); 47.3 (t); 77.3 (d); 124.1 (s); 130.5 (d); 131.5 (d);
‡
134.6 (d); 162.0 (s). MS (electrospray): 327.1 (M ). Anal. calc. for C20H23BF4SO2: C 57.95, H 5.59; found:
C 57.81, H 5.71.
Ethylide 13b. To a suspension of 12b (2.10 g, 5.0 mmol) in EtOH (200 ml), Et3N (2.8 ml, 20 mmol) in EtOH
(100 ml) was added dropwise at 08 within 30 min. The mixture was kept at 08 for 90 min with stirring and then
poured into ice-water (900 g). The white suspension was extracted with CH2Cl2 (3 Â 150 ml) and the extract
dried (MgSO4) and evaporated: 13b (1.65 g, 100%). Pale-yellowish viscous liquid which solidified after 1 h to
afford a colorless solid. IR (CHCl3): 3066w, 2998s, 2936s, 1610s, 1477w, 1377w, 1335s, 1301m, 1133s, 1053m.
1H-NMR (200 MHz, CDCl3): 1.10 ± 2.02 (m, 10 H); 3.40 (br. s, 1 H); 4.60 ± 4.75 (m, 1 H); 7.38 ± 7.60 (m, 10 H).
13C-NMR (50 MHz, CDCl3): 24.2 (t); 25.7 (t); 32.5 (t); 70.3 (d); 73.8 (d); 127.9 (d); 129.5 (d); 130.7 (d); 136.7
‡
(s); 169.4 (s). MS 326 (1, M ), 199(5), 188(5), 187(16), 186(100), 185(50), 184(23), 152(6), 117(13),
109(5), 100(5), 99(9), 92(9), 83(22), 77(13), 69(5), 65(7), 55(14), 51(18), 50(5). HR-MS: 326.1338
‡
(C20H22O2S ; calc. 326.1340).
3. Transition-Metal-Catalyzed Cyclopropanation of Olefins. 3.1. Catalysts. [Rh2(OAc)4] was purchased from
Pressure Chemical Company, Pittsburgh. The chiral Cu-semicorrin catalyst 7 was synthesized as described in
[22]. The synthesis of the chiral RhII catalysts has been described: The procedure of [23] was used for [Rh2{(2S)-
mepy}4] (8); [Rh2{( )-(R)-bnp}4] (9) was prepared as described in [24] and [Rh2{( )-(S)-ptpa}4] (10) according
to [25].
3.2. General Method for Olefin Cyclopropanation. To a soln. of catalyst (0.02 mmol) and olefin (10 mmol)
in 1,2-dichloroethane (DCE, 10 ml) at the appropriate temp., 3a or 4 (1.00 mmol) in DCE (5.0 ml) was added
dropwise within 16 h, by means of a syringe pump. In the case of the Cu-catalyzed reactions with 3a, the catalyst
was activated with a drop of EDA (4). After the addition, the mixture was stirred for an additional 4 h under
reflux. The mixture was filtered through a thin layer of silica gel to remove the catalyst, the filtrate evaporated,
and the mixture directly analyzed by GC to determine the product and enantiomer composition.
3.3. Separation and Characterization of Cyclopropanecarboxylates. The cyclopropane carboxylates 6a ± g
were identified by comparison of their spectral data and GC retention times with data available from previous
studies in this laboratory [16][26] or available in the literature (see also Table 5).
4. Intramolecular Cyclopropanation of Ylide 13a: (1R,5S)-3-Oxabicyclo[3.1.0]hexan-2-one (14). To
[Rh2{(2S)-mepy}4] (19 mg, 0.02 mmol) in refluxing DCE (10 ml), 13a (0.35 g, 1.20 mmol) in DCE (5.0 ml)
was added dropwise by means of a syringe pump within 14 h. The crude mixture was filtered through a thin layer
of silica gel. Flash chromatography (silica gel, petroleum ether/AcOEt 3 :1) afforded 14 (47 mg, 40%), with an
ee of 69% (with LIPODEX E, 1208). For results under different reaction conditions, and with allyl diazoacetate
(15), and determination of absolute configuration [27], see Table 4.
5. Intramolecular CH Insertion of Ylide 13b: Hexahydrobenzofuran-2(3H)-one (16). The previously dried
(activated molecular sieves) 13b (0.31g, 0.96 mmol) in DCE (5.0 ml) was added dropwise within 3.25 h to
[Rh2{(2S)-mepy}4] (18 mg, 0.02 mmol) in refluxing DCE (20 ml). After the addition, the mixture was refluxed
for an additional hour. The catalyst was filtered off. GC analysis of the crude mixture revealed the presence of
cis- and trans-16 as a 73 :27 mixture. Flash chromatography (silica gel, hexane/Et2O 5 :1 afforded 11.5 mg (8.5%)

944
Helvetica Chimica Acta ± Vol. 82 (1999)
Table 5. Diastereomer and Enantiomer GC Separation of Cyclopropanation Products 6 and 14, and of Insertion
Product 16
No Product
GC Column
T
Ref.
6a Ethyl 2-phenylcyclopropanecarboxylate
6b Ethyl 2-pentylcyclopropanecarboxylate
6c Ethyl 2-vinylcyclopropanecarboxylate
6d Ethyl 2-(2-methylprop-1-en-yl)cyclopropanecarboxylate
6e Ethyl 2-methyl-3-phenylcyclopropanecarboxylate (2,3-trans) Supelco b-DEX 120
6f Ethyl 1-(trimethylsilyloxy)bicyclo[3.1.0]hexane-6-carboxylate Supelco b-DEX 120
6g Ethyl 2-ethyl-3-methylcyclopropanecarboxylate (2,3-trans)
14 3-Oxabicyclo[3.1.0]hexan-2-one
16 Hexahydrobenzofuran-2(3H)-one
Supelco b-DEX 120
Macherey Nagel LIPODEX E 508 [29]
Supelco b-DEX 120
Supelco b-DEX 120
1208 [29]
558 [29]
808 [29]
1108 [30]
808 [31]
558 [29]
Supelco b-DEX 120
Macherey Nagel LIPODEX E 1208 [27]
Macherey Nagel LIPODEX E 1208 [28]
of 16 with an ee of 93 (cis-isomer; (3aS,7aS)) and 85% (trans-isomer), as determined by GC (LIPODEX E).
For results under different reaction conditions, and with cyclohexyl diazoacetate (17) [9c][28], see Table 4.
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Received February 19, 1999